I was going to post this in my FM notch filter thread however I decided to separate it. I'm curious if anyone knows of similar band filters for 900 mhz without also wiping out public safety systems in the 800 mhz band?
Unfortunately I recently found out that I happen to live within a mile of a few high power 300-1000w pager systems that operate near 930 mhz which may be impacting my reception abilities to pick up a neighboring county's trunking system due to interference they likely cause.
I'm in the same boat with two high power 929 and 931 MHz paging transmitters about a half mile from me.
I asked Par Electronics if they would consider building a filter for that range. They did and it worked fantastic for attenuating the 929 to 932 paging band. The filter is in the same housing as their other popular filters for scanner problems and it's performance was also about the same as their VHF filters when I ran the 930 filter through some tests.
I think the cost was the same or only $10 dollars more for this custom filters over their normal designs.
Did it work or help? I must say this filter did indeed help with signals in the 800 and 900 MHz bands but only on my GRE designs which include the newer Whistler TRX1 and 2 models. All my Uniden's saw no noticeable benefit from placing this filter inline. If anything, they could have impacted very weak signals due to insertion loss but in my case, they did not seem to hurt anything with the Uniden's if I left the filter inline.
I later changed my antenna arrangement and now have all the GRE designs regardless if they say RadioShack, GRE or Whistler, on one Stridsberg 8-port multi-coupler and the Uniden's on another couple 8-port couplers. The 900 paging filter as well as VHF paging filters are inline before the 8-port for the GRE designs and just a single VHF filter for 152 MHz remains inline for the two multi-couplers that feed the Uniden models.
Uniden seems to have pretty decent front end filtering over the GRE designs. I rarely need the 152 MHz paging filter for the Uniden's as it also reduces the signal from two of our statewide VHF P25 sites that have voice and control channels in the same 152 MHz range as the paging signals. One must use filters here with caution but they do usually work to reduce the powerful paging signals to a level the GRE or Uniden's AGC circuits can handle and still leave enough signal to monitor systems in that range.
Luckily the FCC does not allow anything but paging in the 929 MHz area so filters will only help if you seem to be getting intermod or desense from nearby 929 to 932 MHz paging signals.
Probably the easiest test you can try needs two receivers (more if you have more than one 900 MHz paging source). One scanning the 8 or 900 MHz trunked or analog system you want to hear and another radio tuned to just the 900 MHz paging signal. If you notice bad or poor reception of the voice system you want to monitor only when the paging site is on the air, then a filter may indeed help.
Some of these paging sites have such a high duty cycle that makes catching them off the air a hard thing! Then when they do drop off the air, you have to hope the signals you do want are on the air! That one can be tricky.
That's probably the easiest and cheapest test you can try to do to determine if a 900 MHz paging filter is needed. If you don't hear any improvement when the paging signal is off the air, a filter may be a waste of money.
I also have an antenna feeding another pair of multicouplers that have no filters at all. These feed my communications receivers which are mostly Icom's like the R7000, R9000 and newest R8600 and almost all models in between including many of Icom's portables. I wish scanner makers could make bulletproof front ends like seem to be in higher quality comms receivers.
This is my experience with a notch filter for the common 929 to 932 MHz paging range. If you wish to pursue this, Google Par Electronics and give them a call. Tell them you need a filter for that range and they will build it. Mine even has a custom label on the filter so I can distinguish it from all the other Par filters I own as they all look identical!
Par gave the custom filter they made for me a Part number of UHFSYM(929-932)HT.
The outside of the housing looks identical to their other filters of this type but you can see that the two adjustment caps are of a different design over their VHF filters. It appears to still be a three cavity filter which is also their standard notch filter design. Who knows what the inside yields, I'm not going to bust it open to see!
Mine is fitted with the standard BNC fittings that are used on their regular VHF and UHF filters. They may offer N type connectors as well but for reception only, there is not that much of a difference between the two connector types and BNC does not really introduce much more loss over a good quality N connector.
If your coax needs to also feed higher frequencies, then filters with N connectors may be wise but for scanners, the BNC connectors should be just fine.
When I'm trying for weak signals above 1 GHz on the Icom's, I remove any multicouplers, filters etc and hook a feedline directly to the radio so there is no chance of anything causing loss.
Hope this helps.
